Power plants can employ gas turbines with heat recovery steam generators (HRSGs) that may use thermal energy in the exhaust gas turbines to generate steam for power generation or process use. Examples of an HRSG and use of an HRSG may be found in U.S. Patent Application Publication Nos. 2013/0180228, 2013/0180696, 2012/0240871 and 2011/0048010 and U.S. Pat. Nos. 7,353,654, 6,957,630, and 5,924,389. An HRSG may operate at very high temperatures during normal operation at steady state conditions and an inlet area of the HRSG may operate at a temperature that is substantially greater than a temperature of fluid passing out of an outlet of the HRSG. Further, there is often a substantial difference in the temperature within the HRSG as compared to the ambient temperature outside of the HRSG.
The current technology utilized for hot cased HRSGs often experience problems after one to two years of operation. For instance, hot cased HRSGs have employed external reinforcement designs that exhibit failures between stiffeners and the casing of the inlet duct or main casing of the HRSG. Examples of such failures can include cracking of certain structures. Deformation or distortion between the casing and other external elements such as external stiffeners may also occur. The diagonal bracing may also deform or experience cracking where the diagonal bracing is attached to a wall of the HRSG. In addition, the casing to casing connections between adjacent walls of an HRSG may crack allowing hot gas within the HRSG to escape to the atmosphere. To resolve such issues, an HRSG is often required to be shut down for repair within its first couple of years of service.